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Reverse-Engineering Exploits from Patches

Abstract
The automatic patch-based exploit generation problem is: given a program P and a patched version of the program P', automatically generate an exploit for the potentially unknown vulnerability present in P but fixed in P'. In this paper, we propose techniques for automatic patch-based exploit generation, and show that our techniques can automatically generate exploits for vulnerable programs based upon patches provided via Windows Update.

In many cases we are able to automatically generate exploits within minutes or less. Although our techniques may not work in all cases, a fundamental tenet of security is to conservatively estimate the capabilities of attackers. Thus, our results indicate that automatic patch-based exploit generation should be considered practical. One important security implication of our results is that current patch distribution schemes which stagger patch distribution over long time periods, such as Windows Update, may allow attackers who receive the patch first to compromise the significant fraction of vulnerable hosts who have not yet received the patch. Thus, we conclude update schemes, such as Windows Update as currently implemented, can detract from overall security, and should be redesigned.

What does this mean?
Attackers can simply wait for a patch to be released, use these techniques, and with reasonable chance, produce a working exploit within seconds. Coupled with a worm, all vulnerable hosts could be compromised before most are even aware a patch is available, let alone download it. Thus, Microsoft should redesign Windows Update. We propose solutions which prevent several possible schemes, some of which could be done with existing technology.

Abstract
The automatic patch-based exploit generation problem is: given a program P and a patched version of the program P', automatically generate an exploit for the potentially unknown vulnerability present in P but fixed in P'. In this paper, we propose techniques for automatic patch-based exploit generation, and show that our techniques can automatically generate exploits for vulnerable programs based upon patches provided via Windows Update.

In many cases we are able to automatically generate exploits within minutes or less. Although our techniques may not work in all cases, a fundamental tenet of security is to conservatively estimate the capabilities of attackers. Thus, our results indicate that automatic patch-based exploit generation should be considered practical. One important security implication of our results is that current patch distribution schemes which stagger patch distribution over long time periods, such as Windows Update, may allow attackers who receive the patch first to compromise the significant fraction of vulnerable hosts who have not yet received the patch. Thus, we conclude update schemes, such as Windows Update as currently implemented, can detract from overall security, and should be redesigned.

What does this mean?
Attackers can simply wait for a patch to be released, use these techniques, and with reasonable chance, produce a working exploit within seconds. Coupled with a worm, all vulnerable hosts could be compromised before most are even aware a patch is available, let alone download it. Thus, Microsoft should redesign Windows Update. We propose solutions which prevent several possible schemes, some of which could be done with existing technology.